The invention is directed to a circuit arrangement for triggering a safety system, particularly in an air bag system.
Such a circuit arrangement when used in a motor vehicle air-bag system, usually has a series branch having a tripping device and two series-connected release switches per air bag. These two release switches are actuated by two delay sensors acting independently of one another, so that a tripping only occurs in response to both delay sensors.
When an air bag is provided for a driver and a front seat passenger in a motor vehicle, then two such series branches are required. The two series branches are connected parallel to one another and are supplied with voltage from a common energy source, normally the vehicle battery. Such a circuit arrangement is disclosed, for example, by European patent No. 0 022 146.
Chemical detonating caps triggered by an electrical current flux are usually employed as tripping devices for motor vehicle air bags. As set forth above, the detonating caps for the driver air bag and the front seat passenger air bag are connected in parallel. Due to different switching times of the release switches and different reaction times of the detonating caps themselves, their tripping does not ensue simulateously in case of a crash of the vehicle. After the tripping of the first detonating cap, however, a reliable ignition of the second detonating cap is only possible when the first remains in a high-impedence state after ignition.
Tests that have been carried out with such detonating caps have shown that this is not always the case. In some instances, detonating caps leave conductive connections behind after ignition, so that the energy source is shorted and, thus, an ignition of the second detonating cap is impossible.